1. Technical Field
The present invention relates to a spotting pin for spotting solutions containing biomolecules on a support in the process of manufacturing biochips.
2. Background Art
Biochips are conventionally manufactured by spotting solutions containing biopolymers, such as multiple kinds of DNA, RNA, proteins, or oligonucleotides, on a support, such as a slide glass or a nylon membrane. In such a manufacturing process, spotting pins are used. Various kinds of spotting pins have been developed, including a split-type spotting pin capable of sequential spotting operations based on capillary action, such as that observed in a fountain pen tip. Another example is a solid-type spotting pin in which a spotting solution is caused to adhere to the pin tip before each stamping. The solid-type spotting pin is advantageous in that it is easy to wash and that it wastes less spotting solution. However, it has been difficult to sequentially create uniform spots and produce large quantities of biochips with uniform quality using the solid-type spotting pin. This problem is being overcome in recent years, as evidenced by JP Patent Publication (Kokai) No. 2000-15272 A1. This describes a spotting pin with a pin head on which a cross-shaped groove is formed in order to increase the amount of spotting solution that can adhere to the pin head.
FIG. 12 is a perspective view of the tip of a conventional flat-cut pin that is cut in parallel to the contact surface. The flat-cut pin is used when spotting a solution on a water-absorbing support, such as a nylon membrane. It has the problem that it cannot create spots with circular edges and a stable shape if the spotting speed is high. FIG. 13 is a perspective view of the head of a conventional spotting pin (V-cut pin) in which two V-shaped grooves are formed in the shape of a cross on the head of the body, which is substantially cylindrical in shape, with each V having a wedge angle of 90xc2x0. The V-cut pin has four projections 131 to 134. The projections are substantially triangular-pyramidal in shape, each having an apex located on the external surface of a substantially cylindrical body 130. The V-cut pin forms a spot that tends look like a square, as shown in FIG. 14, and its shape is unstable. If identically shaped spots cannot be obtained, the reproducibility or analysis of an experiment utilizing a biochip may suffer.
Furthermore, there is a need for a technique that enables spots to be formed at high densities, because multiple kinds of biomolecules being spotted in a narrower area would not only allow large quantities of gene expression to be analyzed at once, for example, but would also help reduce the amount of samples used. For this purpose, a spotting pin is required that is capable of stamping small identically shaped spots in a stable manner.
It is therefore an object of the invention to provide a spotting pin capable of forming spots with desired diameters in a sequential and stable manner on a biochip support, such as a slide glass or a nylon membrane.
The above object is achieved by a spotting pin according to the invention in which the head of the pin in which a solution is held is shaped in an advantageous manner.
In one aspect, the invention provides a spotting pin comprising a bar-like body and four projections formed on the head of the body, each of the projections formed in the shape of a top portion of a quadrangular pyramid. The apexes of the quadrangular pyramids constituting the projections are located inside a virtual plane extended from the peripheral wall of the body. This spotting pin makes it possible to spot a spotting solution containing biomolecules on a support, such as a slide glass or a nylon membrane, sequentially and stably, and to obtain spots of identical shape.
The tip of each quadrangular pyramid constituting a projection is preferably cut to be in a plane perpendicular to the central axis of the body. By thus cutting the tip, the possibility of the spotting pin and/or the support being damaged when the former comes into contact with the latter can be reduced.
Of a plurality of wall surfaces possessed by two adjacent projections, the two wall surfaces located toward the center of the body are in a first common plane, while the two wall surfaces located farther from the center of the body are in a second common plane.
The first common plane preferably intersects a plane perpendicular to the central axis of the body at an angle of between 30xc2x0 and 60xc2x0. The second common plane preferably intersects the plane perpendicular to the central axis of the body at an angle of between 30xc2x0 and 60xc2x0. The wedge angle formed by the first and second common planes is preferably in the range of 60xc2x0 and 120xc2x0. The distance between the apexes of quadrangular pyramids constituting adjacent projections may be in the range of 50 to 250 xcexcm.
The biomolecules that can be spotted by the spotting pin of the invention are not limited to DNA. The inventive spotting pin can be used in spotting any kind of biomolecule, such as RNA, proteins, or mixtures thereof, on a support such as a slide glass or a nylon membrane.